[Build] Untangle Span.h

[cecille]

Build issue(s)

Right now Span.h isn't included in the support library. This appears to be on purpose as there are some strange dependencies that cause problems with the darwin logging library. We could potentially pull it out into its own source set with proper dependencies, which would make adding span a lot easier because right now you have to add the config, nlassert and optionally the pigweed tokenizer to get span support. This should be bundled. But it also then requires that the code utils be pulled out into their own set.

Platform

all

Anything else?

No response